With a continuously growing population, it is becoming increasingly difficult to meet the world's energy needs as well as to control carbon emissions to kerb greenhouse gas emissions that are considered responsible for global warming phenomena. These concerns have triggered a drive towards more efficient electricity use in an attempt to reduce energy consumption.
One such area of concern is lighting applications, either in domestic or commercial settings. There is a clear trend towards the replacement of traditional incandescent light bulbs, which are notoriously energy inefficient, with more energy efficient replacements. Indeed, in many jurisdictions the production and retailing of incandescent light bulbs has been outlawed, thus forcing consumers to buy energy-efficient alternatives, e.g. when replacing incandescent light bulbs.
A particular promising alternative is provided by solid state lighting (SSL) devices, which can produce a unit luminous output at a fraction of the energy cost of incandescent light bulbs. An example of such a SSL element is a light emitting diode.
A drawback of SSL element-based lighting devices is that individual SSL elements have a much lower luminous output than e.g. incandescent, tungsten halogen or fluorescent light bulbs, such that it is necessary to include multiple SSL elements in a single lighting device such as a light bulb to obtain the required luminous output levels. However, this is generally perceived to negatively affect the appearance of the lighting device, which hampers the market penetration of such lighting devices, although recently the emergence of so-called chip-on-board (COB) SSL elements, e.g. COB LEDs, in which multiple SSL chips are packaged together as one lighting module such that in use the luminous surface of the lighting device gives the appearance of a single lighting panel, have addressed this problem to a large extent.
Another problem hampering the penetration of the consumer markets by such lighting devices is that it is far from trivial to control the shape of the light output of such devices, at least in a cost-effective manner. This is a particular problem when a highly directional light output is required, e.g. a light bulb having a small beam angle, e.g. a beam angle of less than 30°. Beam angles can be controlled by the inclusion of optical elements such as Fresnel lenses and collimators into the lighting device. For instance, Japanese patent application with publication number JP 2011-192494 A discloses a Fresnel lens for a lighting system having a refractive lens portion and a reflective lens portion. The Fresnel lens further comprises a frame for placing the lens on a substrate of the lighting system.
However, an inverse correlation exists between the beam angle and the size of the optical elements required to achieve the desired beam angle. This means that for small beam angles, e.g. beam angles of 25° or 15°, large size beam shaping elements are required. In many small lighting devices such as compact light bulbs, there is insufficient space to accommodate optical elements such as the aforementioned prior art Fresnel lens.